Fine structure of the neurons of the posterior horn in the rat spinal cord

The region of the posterior horn of the spinal cord in the lumbosacral region of the rat was studied with the electron microscope. This zone contained neurons, astrocytes, oligodendrocytes and blood vessels. The neurons possessed irregular nuclei which occupied a large portion of the cell. The cytoplasm contained elaborate smooth surfaced membrane systems. The rough surfaced endoplasmic reticulum was small in amount and did not possess an orderly arrangement. Electron dense bodies were invariably found within the neurons. The morphological features, such as an extremely irregular nucleus and elaborate cisterns of smooth surfaced reticulum, indicate a well developed nucleocytoplasmic transport mechanism in the neuron. The vascularity of the area was evidenced by the presence of numerous blood vessels which generally had a perineuronal position. Pericytes were invariably found in close relationship to the endothelial cells of the blood vessels. The nucleus of the pericyte was remarkably dense. The cytoplasm of these cells was extremely attenuated and almost encircled the blood vessels.